Nutrient Digestion and Digestibility Flashcards
what is nutrient digestibility
- chemical analysis of feed provides information on nutrient composition
- no information on digestibility in digestive tract (extent of digestion important
- indication of bioavailability of nutrients (nutrients that is available for metabolism)
what is digestibility
- the proportion of a feed that is not excreted in the feces and, therefore is assumed to have been absorbed
- major determinant of nutritional value of feeds
digestible matter + undigestible matter = 100%
what is the concept of digestibility
high digestibility = high nutritional retention = high performance (positive for economics, less so for environment (manuer = nitrogen and phosphorus)
low digestibility = low nutrient rentention = poor performance
what are the methods of measure for feed digestibility
- in vivo
- in sotu
- in vitro
what is in vivo
- total fecal collection
- indicator method
what is in situ
- nylon bag
what is in vitro
- tilley and terry method
- gas prodcution
- enzymes
- regression using chemical analysis
what are step in vivo measurement of digestibility
- test feed or diet given to animal in known amounts for several days - 4-14 adaption period (4-7 days to measure feed intake then collect feces)
- 4-6 animals fed test or diet, digestibility differs; statistical analysis requires replication (consistent feed intake; time of feeding)
- can use males of females
- housed in metabolism crates or stalls, measure fecal output
why do you need an adaption period for feed
- allow time for old feed to be totally excreted (so only test feed is in the diet)
- might take animals GI a bit of time to adapt to the new feed - microorganisms
- feed intake might go down = environmental adaptation to new feed
what are metabolism crates
- sheep and pigs- adaptation periods
- fecal collection - fecal bags or tray behind animal
- urine - delivered by funnel into collection Jar below
how do you use digestibility for total fecal collection
- determine DM % and nutrient content of test feed ( CP crude fat NDF ADF)
- feed animal in metabolic crate, measure FI
- collect total fecal output
- determine DM % and nutrient content in feces
- determine total DW or nutrient intake and total DM or nutrient output in feces
what is the difference between apparent and true digestibility
- most measurements of digestibility are apparent nutrient digestibility
- enzymes + sloughed-off epithelial cells + microbial cells in feces = endogenous losses
- when we dont account for endogenous loss = apparent
- when we do account for endogenous loss = true protein ( true should always be higher, because in apparent you over estimate protein)
what are indirect measurement of digestibility
- some feed ingredients cannot be fed as sole feed ( 100% grain to a ruminant (rumen acidosis) or 100% fat to any animal)
- measure digestibility indirectly using two digestibility trials
- first, determine digestibility of a basal diet which can be fed at the 100% level (the only feed the animal is getting)
- then combine the basal with the test ingredient and measure the digestibility of the basal diet and the test ingredient in combination
what is step 1 in indirect measurement of digestibility
- determine digestibility of the basal diet
- 60% digestibility of alfalfa
what is step 2 in indirect measurement of digestibility
- determine the digestibility of 50/50 alfalfa/grain (5kg each on DM basis)
- fecal output = 2.5 kg
- partition the feces source
- 5 kg of alfala = 2 kg of feces (calculation)
- 10kg of feed = 2.5 feces by test
- 5 kg of grain = 0.5 kg feces by difference
- ## digestibility of grain
